Corrosion inhibitors for cuprous tetrachloroaluminate complexes

ABSTRACT

A method is described wherein soluble compounds of antimony, arsenic, and bismuth are dissolved in aromatic hydrocarbon solutions containing cuprous halide-Lewis acid combinations such as cuprous tetrachloroaluminate to prevent the pitting corrosion of carbon steel. Particularly the method is useful in combination with a process for ligand recovery by means of complexing with aromatic sorbent solutions containing said cuprous tetrachloroaluminate complexes.

Elnited States Patent 11 1 Horowitz et al.

1 1 Sept. 11, 1973 CORROSION INHIBITORS FOR CUPROUS TETRACHLOROALUMINATE COMPLEXES [75] Inventors: Hugh H. Horowitz, Elizabeth;

Charles E. Jahnig, Rumson, both of NJ.

[73] Assignee: Esso Research and Engineering Company, Linden, NJ.

[22] Filed: June 2, 1972 [21] Appl. No.: 259,258

[52] U.S. CI. 260/677 A, 260/6815, 260/6665,

208/47 [51] Int. Cl C07c 7/00, C07c 11/12 [58] Field of Search 260/677 A, 683.15, 260/6815, 666.5, 683.51

[56] References Cited 7 UNITED STATES PATENTS 3,592,865 7/1971 Long et al 260/677 2,431,715 12/1947 Wachter 260/6835! 2,436,918 3/1948 De Forest 118/11 3,249,075 5/1966 Nelson et a1 110/1 Primary ExaminerDelbert E. Gantz Assistant Examiner-Juanita M. Nelson AttorneyLeon Chasan et a1.

[57] ABSTRACT 12 Claims, No Drawings FIELD OF THE INVENTION This invention relates to an improvement in the process for ligand recovery which utilizes complexing of the ligands with aromatic sorbent solutions of cuprous halide-Lewis acid combinations such as cuprous tetrachloroaluminate. The improvement comprises the inclusion in said sorbent solutions of soluble components of antimony, arsenic and bismuth which when dissolved in said solutions prevent the pitting corrosion of carbon steel.

More particularly, it has been found that when operating a ligand recovery process by means of the employment of aromatic sorbent solutions of cuprous tetrachloroaluminate, tetrafluoroborate, hexafluorophosphate, tetrabromoaluminate, tetrachloroborate, mixed chloro and bromo borates and aluminates and the like, that when said process is operated in apparatus containing carbon steel and other ferrous materials, that the aromatic cuprous salt solutions cause corrosion. The rate of corrosion ,is slow but nevertheless pits form under the deposited copper particles which result from what is believed to be the following series of reactions. Fe ZAICI," FeCl, -1 2AICI, 2e

DESCRIPTION OF THE PRIOR The prior art reports that Group V metal compounds have been employed in .the inhibition of corrosion of various ferrous metals. Particularly in U.S. Pat. No. 2,431,715, the prevention of corrosion in hydrofluoric acid (HF) catalytic organic reactions is described. The problem of corrosion, due to the presence of HF and small amounts of water, can be overcome by the addition of arsenic, antimony and bismuth compounds. In U.S. Pat. No. 2,436,918, a method is disclosed whereby soluble arsenic compounds are employed to prevent the attack by acid on the ferrous parts of a steel casing section employed in well drilling. Finally, in U.S. Pat. No. 3,249,075, patentees discuss the corrosion caused by molten ash deposits in various furnace operations. The patentees teach the use of mixtures of antimony I with siliceous material and antimony halides aredisclosed to be used in combination with siliceous materials as coatings for the furnace walls to prevent corrosion by the moltenash deposits.

The process over which the present invention is an improvement, is adequately described in Ser. .No. 756,925 now U.S. Pat. No. 3,592,865. While the process for ligand separation .is therein disclosed; the patentees of this process did 'not' discuss the problem 'of carbon steel corrosion caused by the use of the cuprous tetrachloroaluminate complexes employed in their process. Moreover, while the prior art teaches the use of complexing solutions has made a significant contribution to the art.

SUMMARY OF THE INVENTION In accordance with the present invention, an improved process for the separation and recovery of complexible ligands by selectively complexing them with aromatic sorbent solutions of cuprous tetrachloroaluminate is disclosed, wherein the improvement.

comprises incorporating into the liquid sorbent solution an effective amount of a corrosion inhibitor selected from the group consisting of soluble compounds of Group V metals such as antimony, arsenic and hisprises dissolving into the sorbent solution an effective amount of corrosion inhibitors such as the halides of arsenic, antimony and bismuth. In another preferred embodiment triphenyl compounds of the metals, soluble in the sorbent solutions, are also useful as corrosion inhibitors.

The process then of the invention is one wherein various complexible ligands may be recovered in a ligand exchange process by contacting the feedstream containing the complexible ligands with an aromatic sorbent solution comprised of a cuprous aluminum halide, particularly usefulisthe cuprous tetrachloroaluminate whereby all or substantially all of the complexible ligands are complexed by the sorbent. The complexed ligands, thereafter may be recovered by contacting the complex with an exchange ligand,.which is a ligand which forms a more stable complex with the complexing solution than the ligand to be recovered, and the exchange process is continued'until all the desired complexible ligands have been recovered. Another way in which the desired ligand is separated is by means of accordance with the method set forth in Ser. No.

805,912, now U.S. Pat. No. 3,65 l,l59 which is herein incorp'or'atedby reference. The invention is also applicable toother cuprous halide Lewis acid salt combinations such as, 'CuBfi, 'CuBCh, CuPF., CuAlBr,, CuAlCLBr, (where the sumof r-l-y is four) and their mixtures and the like.

The aromaticv solvent employed is one which may contain specific multi-ringed, high boiling, low melting aromatic solvent compositions, in a major amount together with a minor amount of a single-ringed, strongly complexing, high boiling aromatic. More particularly, the preferred solvents are described adequately in copending application Ser. No. 259,077.

The present process wherein effective amounts of the various above-described corrosion inhibitors are included in the sorbent solvents is amenable for the separation and recovery of a wide variety of complexible ligands. Illustrative of the complexible ligands which may be recovered by means of the present process are olefms, acetylenes, aromatics, carbon monoxide and the like. More specifically, unsaturated hydrocarbons can be acetylenes such as C C acetylenes, preferably C -C acetylenes, for example, acetylene, methyl acetylene, ethyl acetylene, dimethyl acetylene, vinyl acetylene, etc; monoolefins such as C -C monoolefins, preferably C C, more preferably C C, monoolefins, most particularly ethylene and propylene; conjugated diolefins such as C,,C conjugated diolefins, preferably C -C for example butadiene, isoprene and the like; polyolefins such as C C,,,, preferably C,,-C polyolefins, for example, cyclododecatriene, cyclooctadiene, cyclic olefins and alicyclic olefins, such as C -C preferably C -C for example, cyclopentene, cyclohexene, cyclooctene, etc; aromatics such as C,,-C,, aromatics, preferably C,,C aromatics, for example, benzenes, toluenes, and xylenes; cumulative diolefins such as C --C cumulative diolefins, for example allene; preferably, however, the process is applicable for the separation of light monoolefrns such as C C, monoolefins, and other complexible ligands, such as C C acetylenes, carbon monoxide and C,,C aromatics.

Generally the complexible ligands to be separated and recovered by the process are contained in a feedstream in admixture with other components which are not as preferentially complexed. For example such feedstreams as ethane-ethylene or propane-propylene can be treated to concentrate the olefin.

The corrosion problem arises because the copper in materials such as cuprous tetrachloroaluminate, is more noble or less active than the iron in carbon steel, and therefore tends to become metallic copper while the iron is oxidized to ferrous ion. The following half cell reactions can occur:

The deposition of the copper from the complexing solution causes the pitting of the carbon steel vessel. By incorporating soluble compounds of the metals such as the halides of Group VA metals, i.e., arsenic chloride- ,antimony chloride, bismuth chloride and the like, as well as various triphenyl compounds of these metals, the pitting corrosion caused by the above half cell reactions may be prevented.

Now it has been found that the metals of Group V are useful as corrosion inhibitors in the operation of the present process, however, it must be stated that these metals are not necessarily equivalent in the degree to which they inhibit the corrosion, since some of the metals are more effective in their corrosion inhibiting properties than others. Similarly, the amount of specific inhibitor material to bemaintained within the complexing sorbent solution will vary in accordance with variations and operating conditions in the composition of the metal surface in contact therewith. However, in general, when the metal surface in contact with the reactants com prises a ferrous metal or a carbon steel surface, the concentration of the inhibitor metal to be maintained in the reaction zone will generally range from about 0.05 to about 10 wt. based on the cuprous complex and preferably from about 0.1 to about 5 wt. based on the amount of cuprous complex in solution.

On the metals of Group V antimony, arsenic and bismuth are preferred. As was previously stated the inhibitor metal is preferably employed in the form of a suitable compoundsuitable compounds of the inhibitor metals comprise the metal in chemical combination with one or more of the halides such as the chlorides, bromides and fluorides, for example, antimony chloride, antimony fluoride, antimony bromide, and like halides of arsenic and bismuth. Additionally, triphenyl compounds of the metals are also suitable, triphenyl compounds such as triphenyl arsine, triphenyl stibine and triphenyl bis-muthine are suitable and may in fact be preferable because they exhibit less of a tendency to promote Friedel Crafts-type side reactions. Alkyl and naphthyl compounds may also be suitable; mixed alkyl and aryl compounds of the metals may likewise be used.

The inhibitor material may be independently injected into the system and maintained at various levels depending on operating conditions. Alternatively, the inhibitor material or a compound comprising said material may be employed in the form of an admixture or in chemical combination with organic compounds such as the triphenyl phosphines. Preferably, however, the inhibitor metal will be included in the complexing sorbent solutions prior to the employment of said solutions in the ligand exchange apparatus. It is important for the overall prevention of corrosion that the inhibitor material be maintained in the prescribed concentrations throughout the operation. This is because the subjection of the metal surface to contact with the inhibitor metal prior to or during intermittant stages of operation, will generally not render such surfaces immune to subsequent corrosion by the cuprous tetrachloroaluminate. Since the sorbent solution is generally passed in a continuous stream through the system, the continuous presence of the inhibitor material is thereby necessitated.

The preference of any particular compound of a suitable inhibitor material may be governed by the temperatures, pressures and concentrations of salt used in the process and the nature of the steel used.

DESCRIPTION OF THE PREFERRED EMBODlMENT In a preferred embodiment of the invention described herein, ethylene and propylene are separately recovered from a feedstream as may be obtained from thelight ends section of a conventional stream cracking unit. Such a feedstream from which acetylene and'carbon monoxide may havepreviously been removed, e.g., by cuprous ammonium acetate complexing and conventional carbon monoxide absorption. Such a stream contains methane, ethane, propane and hydrogen in addition to the desirable ethylene and propylene ligands. These desired ligands can be recovered in purities exceeding percent, preferably exceeding 99 percent, by the process of the present invention, wherein the abovedescribed cuprous tetrachloroaluminate complexing solutions are employed and incorporated into said solutions are the effective amounts of corrosion inhibitors.

In this typical processing scheme in which aromatic solutions of cuprous tetrachloroaluminate are utilized, iron coupons employed as, test strips for determining corrosions show an open circuit potential of 9 to -18 millivolts relative to a copper wire in the same solution. By incorporating an amount of antimony chloride into the solution the open circuit potential becomes +30 EXAMPLE 1 Electrochemical Studies In this example, corrosion of carbon steel in aromatic tetrachloroaluminate complexes is measured in a glass cell of about 35 cc capacity. The test piece, usually V4 X rfiinch by 1% inch is centrally mounted on an alliga' tor clip and immersed to a depth of 1 inch in the electrolyte. The test pieces are sandblasted before use. A luggin capillary tip entering the side of the cell with a small opening near the working electrode contained a copper wire reference electrode. (Separate studies had shown that the plating or deplating of copper from a copper-plated wire was reversible in this complex; that is the anodic and cathodic branches of the current voltage curves were continuous and limited only by elec- O trolyte resistance).

The potential of the working electrode relative to the reference electrode was measured with Kiethley electrometer of IO ohms impednace. The impedance of the working-reference electrode circuit was of the order of 10 ohms. The corrosion data on aromatic solutions of cuprous tetrachloroaluminate and other cuprous salts are summarized in Table I. The open circuit or rest potential of the iron coupon, versus the reversible copper potential is given. A negative potential means that the iron is spontaneously dissolving in the solution causing copper metal precipitation. A positive potential indicates that this exchange is thermodynamically unfavorable. The current at zero millivolts versus reversible copper is a rough measure of the rate of corrosion (l mil/yr. approximately equal to 10 micro amps). However, because of film formation the rate of iron corrosion is not very reproducible. Therefore, the sign of the open circuit potential and the existence of anodic current at zero millivolts are considered a qualitative indication that copper deposition is occurring in the absence of an applied potential. The reverse indicates that it is not.

The results of these studies are summarized in Table l, and show that the inclusion of effective amounts of corrosion inhibitors based on Group VA. metals, will prevent copper deposition and the subsequent pitting of any ferrous surfaces such as carbon'steel, in contact with the solutions of CuAlCl material was dissolved in benzene and isopropylbiphenyl solvents. The test equipment for the tests in benzene comprised of 6l00 cc glass tubes connected to a common manifold having a plastic gas expansion bag. Each tube 5 contained a magnetic stirrer. The equipment was assembled and filled in the nitrogen dry box. The tubes were filled about half full with complex and the coupon was held totally immersed under the complex solution suspended from a glass hook. The tubes were then submerged in an oil bath for the test period. The test coupons, before terminating the tests, were visually inspected and were thereafter removed, washed in benzene, followed by acetone, padded dry, and sent for determination fo corrosion and the presence of copper particles.

The results of the test may be found in Tables Ila and Ilb. The test in the benzene solvent was conducted at 176F. for approximately 200 hours. The test conducted in the isopropylbiphenyl solvent was as follows: the carbon steel coupons were hung on glass stirrups in the complex for 402 hours at C. and inert nitrogen atmosphere was passed over the complex. The results are summarized in Tables Ila and Ilb, and show that the addition of an additive reduces the corrosion rate in mils per year of the carbon steel coupons and also prevents the pitting and deposition of copper particles on the coupons.

TABLE II (a) STATIC CORROSION TESTS-BENZENE 176F., on es/crunc Carbon steel Coupons 200 s Hours on Test Inhibitor Corrosion Rate Presence of Cu Milslyr. Particles None 9 Yes 2m. a. she]. 2.4 No

TABLE ll(b) STATIC CORROSION TEST-HIGH BOILIN SOLVENT 135C. Isopropyl Biphenyl CuAlCl Additive Mole on Cu Corrosion Rate Fitting Mils/yr. O,Bi 1.0 2 None Whatis claimed is: 1. An improved process for the separation and recovery of complexible ligands from feedstreams containing said ligands bycontacting said feedstreams with an aro- TABLfiL-PREVENTIbiVb'F"Corr ne DEPosIrIoN AN'orrrTrNG' BY GROUP v AbDITIvEs [Solvent Benzene (0H')] Potential vs. Cu., mv.

Temp Base Treated Base soln. Additive 1 sol'n. soln.

Run No.1

1 1% SbCl; 65 23 +25 .25 -I7 +50 65 l2 +25 65 5 +9 65 17 +1.5 3% (7) SI 65 17 +3 14.. @H 2.5/CuAlCl4 .870 (0aSl +dl tertiary hutyl pyridine" G5 17 +18 1-8.. {DH 2.5/CuAlCh... 1% 01131 65 8 +44 1-9... (01-! 2.5/CuAlCl 075% SbCh 65 -15 +55 1-10 Methyl blphenyl CllAlCh +4.6 mole percent QM 1.4 mole percent SbCl; +6 +11 1 Wt. percent except as specified.

EXAMPLE 2 In this Example several static corrosion tests were conducted, wherein the cuprous tetrachloroaluminate matic sorbent solution containing cuprous halide-Lewis acid salt combinations wherein the improvement comprises incorporating into said aromatic sorbent solution an effective amount of a corrosion inhibitor, selected from the group consisting of soluble compounds of group V metals comprising arsenic chloride, antimony chloride, bismuth chloride, triphenyl compounds of these metals, alkyl and naphthyl and mixed alkyl and aryl compounds of antimony, bismuth and arsenic to thereby substantially reduce the overall corrosion effect of the cuprous salt solution.

2. The process of claim 1 wherein the soluble compounds are triphenyl compounds of said Group V metals.

3. The process of claim 1 wherein the complexible ligands to be recovered are C -C monoolefins.

'4. The process of claim 1 wherein the process is conducted in a temperature ranging from between 80F, and 350F., and at pressures of from 0.1 atmospheres to 30 atmospheres.

5. The process of claim 1 wherein the amount of corrosion inhibitor present in the solution is from about 0.1 to about 5 percent by weight based on the amount of cuprous salt employed.

6. An improved process for the separation and recovery of complexible ligands from feedstreams by contacting said feedstreams with an aromatic sorbent solution containing cuprous tetrachloroaluminate, wherein the improvement comprises dissolving into said solution an amount of a corrosion inhibitor selected from the group consisting of halides of arsenic, antimony and bismuth and mixtures thereof, said amount ofinhibitor being effective to prevent the deposition of copper from the cuprous tetrachloroaluminate solution.

7. The process of claim 6 wherein the amount of corrosion inhibitor required ranges from 0.1 to about 5 percent by weight based on the amount of cuprous tetrachloroaluminate employed.

8. The process of claim 6 wherein the corrosion inhibitor is arsenic chloride, antimony chloride or bismuth chloride.

9. The process of claim 6 wherein the contacting is carried out at temperatures ranging from to about 350F.

10. The process of claim 6 wherein the corrosion inhibitor comprises triphenyl compounds of Group V metals.

11. The process of claim 1 wherein the complexible ligands to be recovered are ones selected from the group consisting of C C acetylenes, C C monoolefins, C --C, conjugated diolefins, C C, aromatics and carbon monoxide.

12. The process of claim 6 wherein the complexible ligands to be recovered are selected from the group consist of C -C monoolefins, C -C acetylenes,

C C, aromatics and carbon monoxide. 

2. The process of claim 1 wherein the soluble compounds are triphenyl compounds of said Group V metals.
 3. The process of claim 1 wherein the complexible ligands to be recovered are C2-C4 monoolefins.
 4. The process of claim 1 wherein the process is conducted in a temperature ranging from between 80*F., and 350*F., and at pressures of from 0.1 atmospheres to 30 atmospheres.
 5. The process of claim 1 wherein the amount of corrosion inhibitor present in the solution is from about 0.1 to about 5 percent by weight based on the amount of cuprous salt employed.
 6. An improved process for the separation and recovery of complexible ligands from feedstreams by contacting said feedstreams with an aromatic sorbent solution containing cuprous tetrachloroaluminate, wherein the improvement comprises dissolving into said solution an amount of a corrosion inhibitor selected from the group consisting of halides of arsenic, antimony and bismuth and mixtures thereof, said amount of inhibitor being effective to prevent the deposition of copper from the cuprous tetrachloroaluminate solution.
 7. The process of claim 6 wherein the amount of corrosion inhibitor required ranges from 0.1 to about 5 percent by weight based on the amount of cuprous tetrachloroaluminate employed.
 8. The process of claim 6 wherein the corrosion inhibitor is arsenic chloride, antimony chloride or bismuth chloride.
 9. The process of claim 6 wherein the contacting is carried out at temperatures ranging from 80* to about 350*F.
 10. The process of claim 6 wherein the corrosion inhibitor comprises triphenyl compounds of Group V metals.
 11. The process of claim 1 wherein the complexible ligands to be recovered are ones selected from the group consisting of C2-C6 acetylenes, C2-C20 monoolefins, C4-C10 conjugated diolefins, C6-C12 aromatics and carbon monoxide.
 12. The process of claim 6 wherein the complexible ligands to be recovered are selected from the group consist of C2-C4 monoolefins, C2-C4 acetylenes, C6-C9 aromatics and carbon monoxide. 